Thawing apparatus is used to thaw frozen food products such as fish products. Such thawing apparatus typically comprises a thawing tank and a rotation axis which extends from an in-feed end of the tank to the other opposite out-feed-end and a water injection unit which injects hot or warm water into the tank at the in-feed end. A large spiral blade is mounted to this rotation axis which extends from the in-feed end to the out-feed-end. The thawing process is based on putting the frozen food products to be thaw into the tank that is filled partly with water at the in-feed end, where the thawing includes moving the frozen food products from the in-feed end towards the out-feed end via the rotating spiral blade. The rotation of the spiral blades ensures that the first fish products that first enter the in-feed end will be the first to reach the out-feed end (“first-in-first-out”). To ensure an optimal temperature in the tank, warm water at some optimal temperature and flow is injected constantly into the tank at the in-feed end of the thawing tank.
The drawbacks with such prior art thawing apparatus is that it is difficult or even impossible to ensure an optimal temperature distribution in the tank. This has the consequences that large ice/fish clusters can easily be formed somewhere in the tank because of uneven heat temperature distribution in the thawing tank. The conveying of the fish products or fish clusters must therefore be stopped, or when the conveyed fish products or fish clusters reach the out-feed-end will not yet been thawed.
Another drawback with the current thawing apparatus is related to thawing shell fish and other small fish products, but until now the frozen shell fish is typically in a form of blocks or clusters (many shell fish products frozen together) that are fed into the thawing tank at the in-feed-end, where also the water injection takes place. In order to avoid that the blocks get stuck together and form a larger clusters, one block at a time is put into the thawing tank and some time must lapse until the second block can be put into the tank. By doing so, the risk that the blocks get stuck together is reduced. This is continued until some preferred amount of shell fish and other small fish products has been put into the thawing tank at the in-feed-end. Since the warm water injection takes place at the in-feed-end, a very rapid cooling takes place there due to the large amount of cooling agent (the blocks) meaning that the heat of the injected water or the flow of the water must be increased. After feeding the shell fish blocks it is awaited until the blocks are thawed. This process typically takes several hours. Subsequently the spiral movement of the spiral blade is initiated and the shell fish and small fish products are conveyed from the in-feed-end towards the out feed end. The problem that frequently occurs during conveying the shell fish/small fish products is that they can easily be clamped between the spiral blade and the bottom of the tank which results in destroying some amount of the shell fish (small) fish during the conveying.
Another process that is worth of considering is a cooling process, which is adapted to cool down food products rapidly, e.g. processed fish that must be cooled down as soon as possible, but that are to be sold as fresh (not frozen). A typical cooling process that is currently used to cool down fish after being processed on board of a ship is to put the fish into tub with ice, and keep in that way until the ship arrives to the harbor. However, if the temperature of the fish is too high when it is put into the tub meaning that the melting of the ice starts almost immediately. There can be many hours or days until the ship arrives the harbor, but in the meantime the freshness of the fish has somewhat diminished and therefore the value of the fish.
US 2006/0225438 discloses a chiller for reducing temperature of buoyant birds, including semi-cylindrical tank that conforms to the perimeter of its auger so that the water can be raised to a water level high above the auger shaft. Streams of water are directed from the pulling side across the lower portion of the tank beneath the auger shaft to the dead side of the tank at intervals along the tank so as to disperse the lower portion of the masses of buoyant birds from the more crowded pulling side of the tank, beneat the auger shaft toward the more vacant dead side of the tank. In that way, the products become more evenly distributed throughout the tank causing more turbulence in the tank. In that way, the rate of heat transfer from the birds is increased thus avoiding having the birds cross over the auger shaft moving backward in chiller into a flowing flight of the auger. This reference is however limited to chilling food products.